Japanese patent publication 2007-93951A (US2007/071489A1) discloses a side seal member that is provided between an end part of a rotatable developing roller and a developing unit housing and that is located adjacent to a developer supply port of the developing unit housing. The side sealing member includes an upstream side seal and a downstream side seal, each being constructed by a two-layered configuration having a sponge base and a felt member on the sponge base.
Because fibers of the felt member are not unidirectional, developer entering the felt member may be moved in a direction away from the supply port by sliding contact between the felt member and the developing roller to cause toner leakage. Because a double-side adhesive tape is used to adhere the sponge base and the felt member together to form each of the seals and thereafter the seals are adhered to the developing unit housing, the attachment of the seals to the developing unit housing is troublesome and time-consuming.